The present invention relates generally to rotary valves and, more specifically, to an improved pin connection of the shaft to the closure member of a rotary valve.
Butterfly valves generally include a disc pivotably connected to the body of the valve by one or more shafts. The shafts are received in the center of the disc on a special hub which is generally integral with the valve. The hubs are either on the backside or the center of the disc. Since it is generally desirable for the disc to be removable from the housing, pins which traverse the disc and the shaft removably secure the shaft to the disc.
One prior art method of securing the shaft to the disc using a pin is illustrated in FIG. 1. The disc 10 receives a shaft 12 and includes a pin 14 threadably received in the disc 10. The longitudinal axis of the pin 14 intersects the longitudinal axis of the shaft 12. Depending upon the size of the shaft and the load anticipated, a pair of pins 14 may be displaced along the axis of the shaft 12 to secure the shaft to the disc. When the shaft and the disc are placed under a torquing load relative to each other from the fluid or the opening and closing motion of the valve, the pin 14 is placed under a shear force. Thus, the pin 14 must be of a given size to operate efficiently under such shear force.
Another prior art method of securing the disc and shaft is illustrated in FIG. 2 and includes a disc 20, a shaft 22 and a pin 24. As can be seen, the pin 24 has its longitudinal axis transverse to the longitudinal axis of the shaft 22. This arrangement in effect is like a cotter pin. As in the prior art assembly of FIG. 1, the assembly of FIG. 2 places the pin 24 under a shear stress when the shaft 22 attempts to rotate relative to the disc 20.
In both prior art assemblies of FIGS. 1 and 2, the opening in the shafts 12 and 22 as well as in the discs 10 and 20 will wear thus there will be a delay or hysteresis effect between the rotation of the shaft and the discs. This is highly undesirable. Merely tightening the pins 14 and 24 will not adjust for this wear of the elements. Thus, there exists the need for a pin connection of a shaft to a disc which is not susceptible to shear forces when the elements are placed under torque and which is adjustable for wear of the elements.